Major animal species, minor bacterial pathogens: a bacterial minority report from different clinical cases in pigs, 2020-2024
Annet Heuvelink* and Jobke van Hout Royal GD, Deventer, the Netherlands
Introduction
GD performs antimicrobial susceptibility (AMS) testing of pathogens from different animal species, both to guide therapeutic treatment and for monitoring purposes. Since the implementation of MALDI-TOF MS for identification of bacteria, the range of bacterial species identified at the laboratory of GD has broadened.
Aim
To review the different ‘minor’ bacterial species identified and their AMS.
Methods
Data collection: ‘Minor’ bacterial species (n ≥ 15 isolates per species) and AMS results were extracted from the Laboratory Information System (LIMS), with all isolates originating from clinically diseased pigs submitted to the necropsy room of GD from 2020-2024. At post-mortem examinations, macroscopic lesions were sampled, and hence only bacterial species apparently associated with these macroscopic lesions were isolated and identified.
MIC results: For each of the selected ‘minor’ bacterial species, minimum inhibitory concentration (MIC) distributions were compiled and percentages of susceptible and resistant isolates were calculated using CLSI veterinary breakpoints (when not available: human-derived) (CLSI VET01S ED7:2024).
Discussion and Conclusions
• Generally, isolates of ‘minor’ bacterial pathogens from pigs were characterized by low MICs of 1st choice antimicrobials tested.
• However, for both Streptococcus subspecies high MIC values were obtained for clindamycin (indicator of lincomycin) (±40% of the isolates), erythromycin (indicator of tylosin) (±40-50%), and tetracycline (±75%). S. chromogenes also had high clindamycin (±55%), erythromycin (±45%), and tetracycline (±40%) MICs. S. chromogenes additionally had high MICs of penicillin (±30%). K. pneumoniae isolates revealed relatively high MICs of tetracycline (±30%).
• MICs of most 2nd and 3rd choice antimicrobials were also relatively low.
• Interpretation of MICs obtained for ‘minor’ pathogens is hampered by the lack of CLSI/VetCAST-defined clinical veterinary breakpoints.
• Pig-specific clinical breakpoints for interpretation of MICs are available for only five bacterial species, for only respiratory disease.
• More veterinary breakpoints are needed for responsible and prudent use of antimicrobials.
Results
Table 1. MIC (%) distribution for Streptococcus dysgalactiae ssp. equisimilis isolates (n=145), 2020-2024.
Table 2. MIC (%) distribution for Streptococcus dysgalactiae ssp. dysgalactiae isolates (n=17), 2020-2024.
Table 3. MIC (%) distribution for Staphylococcus chromogenes isolates (n=16), 2020-2024.
Table 4. MIC (%) distribution for Klebsiella pneumoniae isolates (n=22), 2020-2024.